Android has the same potential, but it's less cohesive a platform and doesn't have the rich app catalog or rich app capabilities that iOS does; its ability to serve as a PC replacement in the near term just isn't plausible. It also lacks some PC capabilities, such as printing, that iOS offers, and the technologies it uses for connecting to displays is poorly implemented and inconsistent.

Android's bigger problem, though, is Chrome OS. Google's Web-only PC platform (delivered on Chromebook laptops and Chromebox PCs) is less capable than any mobile platform, relying on Web apps to do real apps' work. And they simply can't. There's been no progress in Web apps for years, despite Google's championing of the concept. Its own Google Docs, for example, remains essentially stuck. But as long as one part of Google promotes the Web PC vision and another the Android mobile device vision, there's no cohesive post-PC platform at Google for users to count on.

Then there's Windows RT, Microsoft's attempt to leave traditional Windows behind. Well, almost -- it'll run in a protected x86-like environment Office 2013 and Internet Explorer 10, proof that Metro isn't likely to be the post-PC platform in which you can place your trust. Metro's apps are very primitive compared to what's available on iOS and even Android, and the fact that Microsoft basically has to run its core business software outside of Metro on an otherwise Metro-only device shows how unlikely Metro can evolve quickly as a general-purpose platform.

Of course, Google and Microsoft could pull some rabbits out of their hats and change the equation. Maybe iOS won't be the only obvious post-PC platform to begin anticipating a switch to. No matter, what's key is that people are now anticipating a post-PC switch. That's a revolution in the making.

Galen Gruman is an executive editor at InfoWorld focused on mobile and user-facing technologies, an author of more than 40 how-to books, editorial CTO for IDG US Media (InfoWorld's parent company), and an adjunct analyst focused on enterprise mobility at IDC's IT Executive Program.